This invention relates to organic solvent-based inks for piezo inkjet printing and the methods of making and using such inks.
Inkjet imaging techniques have become very popular in commercial and consumer applications. The ability to use a personal computer and desktop printer to print a color image on paper or other receiving substrate has extended from dyebased inks to pigment-based inks. The latter provide brilliant colors and more durable images because pigment particles are more durable than dyes on the receiving substrate.
Thermal inkjet print heads are commercially available from Hewlett Packard Corporation or LexMark Corporation in inkjet printers commercially available from Hewlett Packard Corporation, Encad Inc., Mimaki Corporation, and others.
Piezo inkjet print heads are commercially available from Calcomp (Los Angeles, Calif.), Epson Corporation (Torrance, Calif.), Data Products (Woodland Hills, Calif.), Xaar (United Kingdom), and others. These printheads differ in physical properties such as frequency and drop volume. The inks to be used in them often require different physical properties such as viscosity. Such print heads are used in piezo inkjet printers commercially available from Idanit Technologies, Ltd. of Rishon Le Zion Israel, Raster Graphics of San Jose, Calif., Vutek Inc. of Meredith, N.H., Olympus Optical Co. Ltd. of Tokyo, Japan, and others.
Inkjet printers have been in general use for wide-format electronic printing for applications such as, engineering and architectural drawings. Because of the simplicity of operation, economy of inkjet printers, and improvements in ink technology, the inkjet imaging process holds a superior growth potential promise 5 for the printing industry to produce wide format, image on demand, presentation quality durable graphics.
The components of an inkjet system used for making image graphics can be grouped into three major categories:
1. Computer, software, printer with print head and plumbing components;
2. Ink; and
3. Receiving substrate.
The computer, software, and printer controls the size, number and placement of the ink droplets and transports the receiving substrate. The ink contains the colorant (e.g., pigments) which form the image. The receiving substrate provides the medium that accepts and holds the ink. The quality of the inkjet image graphic is a function of the total system. However, the composition and interaction between the ink and receiving substrate is important in an inkjet system only after the ink has traversed the plumbing of the printer and been jetted through the print head without damage to either the print head or the ink. Good quality is what the viewing public and paying customers want and demand to see. Many other demands are also placed on the inkjet media/ink system from the print shop, such as rapid drying, humidity insensitivity, extended shelf life, waterfastness, and overall handleability. Also, exposure to the environment can place additional demands on the media and ink (depending on the application of the graphic). Typically, outdoor durability includes withstanding temperature extremes, exposure to moisture ranging from dew to rainstorms, and colorfast stability in the face of sunlight""s ultraviolet light.
The chemical formulation of the pigmented inkjet ink has considerable complexity due to the requirement of continued dispersion of the pigment particles in the ink supply vessel and during jetting of the ink, yet rapid drying once the ink has been jetted on to the receiving substrate.
Piezo inkjet inks have distinct advantages over thermal inkjet inks. Thermal inkjet inks are limited to water-based systems. Because of the high temperatures involved in the thermal print head jetting process, the use of binders are limited because such binders form a residue on the heating elements of the print heads, a problem that is called xe2x80x9ckogationxe2x80x9d in the art. The presence of residue results in failure of the print heads to provide quality image graphics, and the need to replace them on a regular basis.
Further, in order to prevent these water-based thermal inkjet systems from drying too early, i.e., while in the print head nozzles, these inks contain a high concentration of glycols or other types of humectant. This high concentration of glycols prevents the inks from drying completely once the thermal inkjet ink is jetted to form the image on the receiving substrate because, as noted above, these inks have essentially no binder in their formulation, which would otherwise have permitted the formation of a film of the ink drops on the receiving substrate after the evaporation of water.
The combination of these jetting and drying conditions for thermal inkjet inks has forced thermal inkjet inks to be jetted onto receiving substrates that have a specialized ink-receptive layer. Several examples of specialized inkjet media are disclosed in U.S. Pat. Nos. 5,747,148; 5,389,723; and 5,472,789. All of these inkjet media concern the issue of the disposition of liquid after jetting has occurred for pigment-based inkjet inks.
Moreover, because thermal inkjet inks cannot have a binder in their formulation, durability from exposure to the effects of the environment for the resulting image graphic is obtained by the use of an over laminate, typically provided by a clear coating of a rapid-drying solution or a film that adhesively laminates to the resulting image.
Piezo ink print heads jet their ink by a mechanical action as opposed to heating. Piezo inks can be aqueous or non-aqueous and can include a film-forming binder. The viscosities of these inks are higher than those of thermal inkjet inks. Thermal inkjet inks typically have viscosities around about 3 to about 5 centipoise (mPaxc2x7sec), whereas pigmented piezo inks typically have a viscosity of from about 5 to about 100 mPaxc2x7sec at 25xc2x0 C. depending on the type of piezo jet print head and the particulars of its specifications and performance.
However, viscosities of piezo inks are orders of magnitude lower than screen print inks used in the printing industry. Screen print inks typically have viscosities of at least about 1000 mPaxc2x7sec at time of usage. In commercially available screen print inks from Minnesota Mining and Manufacturing Company, such inks include pigment, binder, plasticizer, stabilizers, silicone oils, and solvents. The percent solids of such inks are typically between about 30 and 40 percent. In one of such inks, a fluorochemical flow agent is added for assuring complete covering of the image graphic as a clear coating. In other of such inks, to assure porosity and facilitate air passage, a minor amount of silica particles is dispersed. But none of the inks has both a fluorochemical flow agent and dispersed silica particles, because the properties of one would counteract the properties of the other.
Piezo inkjet inks have their own set of problems to overcome to achieve a high quality image with acceptable durability for its intended usage. A variety of others have attempted to develop and market piezo inkjet inks. Among those that use volatile organic solvent systems for delivery of ink through the print head and to the receiving substrate are Salsa brand inks marketed in conjunction with Salsa brand printers from Signtech of San Antonio, Tex.; Crisper brand inks from Precision Color of Newbury, Berkshire, U.K.; and piezo inks from Inkware Corporation of Las Vegas, Nev., USA.
However advanced these other piezo inkjet inks may be, there are complications attendant to how an organic solvent-based piezo inkjet can successfully be jetted through piezo inkjet print heads having drop sizes most often ranging from about 30 to about 70 picoliters (pL), which are common for the print heads used in wide format piezo inkjet printers commercially available from the printer manufacturers identified above. Most particularly, the quality and durability of the resulting image graphic is directly dependent on the ink formulation that navigates the jetting process yet forms an image graphic on the receiving substrate suitable for intended uses.
What the art needs is an organic solvent-based ink that preferably has excellent properties of viscosity, flash point, specific gravity, pigment:binder ratios, solids percentage content, anti-foaming, and flow in order to produce durable image graphics with piezo inkjet print heads that deliver nominally about 20-70 pL drops of ink. The art needs an ink formulation that includes a solvent and additive combination that delivers ink to the print head without damage to the plumbing of the printer, jets the ink through the print head without damage to the print head or the ink, and dries rapidly on the receiving substrate. Each of these properties will be addressed separately.
Piezo print heads can use higher viscosity inks through the print head. This allows for the use of binders and pigments that one could not use at the lower viscosities required of thermal inkjet inks. Also, this allows one to obtain a stable ink film formed on the receiving substrate that can impart durability without the use of a clear coat or over laminate as protection for the resulting image graphic.
Further, because piezo inks of the present invention can contain both a binder and rapidly-drying organic solvents, these inks can be jetted directly onto films without the need of specialized porous receiving substrates as identified above that are used to address the slower drying humectant-containing water systems of thermal inkjet inks.
Inks of the present invention are believed to be able to last outdoors for at least three years without a clear coat or over laminate and for an additional two years if an optional clear coat or over laminate on a selected receiving substrate is used.
Inks of the present invention can form excellent image graphics on conventional polymeric films, such as vinyl films, that are not specially treated with coatings or formulations to aid in the dispensation of liquids used in the inks. Excellent polymeric films for use with inks of the present invention include Scotchcal(trademark) brand films from Minnesota Mining and Manufacturing Company (3M) of St. Paul, Minn., USA.
The present invention solves the problems in the art by providing an ink system having the ability to disperse particulate material, such as pigment particles, in the solvent, permit uninterrupted flow through the piezo inkjet print head, and assure rapid drying of the ink of pigment particles and binder once the ink contacts a conventional polymeric film to form a durable image graphic. The selection and balance of liquids used to assist the pigment particles and binder to form an image graphic unexpectedly produces image graphics not previously produced with piezo inkjet printers.
The present invention has found two different types of materials that can be combined to permit flow through the print head yet rapid evaporation from the receiving substrate. The combination of these flow agents has an unexpected result for the present invention.
It is known that silicone oils can serve as flow agents, e.g., see U. Kaluza, xe2x80x9cFlocculation of Pigments in Paintsxe2x80x94Effects and Causes,xe2x80x9d Progress in Organic Coatings, 10, 289 (1982). Such silicone oils, however, have been found to cause ink running on some conventional substrates with high ink coverage because the oils can slow the evaporation of solvent. Avoiding ink running is critical for a substrate in a vertical position during printing due to the effects of gravity. The route to correction of that problem, the use of more volatile solvents for the ink, encounters the unavoidable problem of limiting the flash point of the inks to remain above about 61xc2x0 C. (142xc2x0 F.), which temperature is significant in regulations involving shipping of volatile chemicals. Thus, a careful balance of flow agents has been found to be needed to inhibit evaporation within the printer but encourage evaporation on the receiving substrate.
One type of flow agent is a fluorochemical surfactant that is efficient in lowering the surface tension of organic solvents. However, it can encourage foaming in an organic solvent. This flow agent is similar to those fluorochemicals used in screen printing inks to provide a continuous layer that is important for clear coatings to protect a finished image graphic.
The second type of flow agent is an antifoaming oil that discourages any inadvertent foaming tendency caused by the presence of the fluorochemical surfactant. The antifoaming oils of this invention are viscous, substantially water-insoluble liquids that can alter the surface tension of a fluid at room temperature. The antifoaming oils used in the present invention are preferably substantially non-drying oils (i.e., they do not significantly absorb oxygen to become hard and resinous upon exposure to air) and are substantially non-film-forming fluids (i.e., they do not generally form a coherent film when a solution of the oil in solvent is coated as a thin layer, and the solvent is evaporated) at room temperature. Such oils preferably are not crosslinked and are generally stable in air. Antifoaming oils suitable for use in this invention include, but are not limited to, mineral oils and silicone oils. A preferred antifoaming oil for use in the present invention is an antifoaming silicone oil. Many antifoaming silicone oils used in screen printing inks have viscosities ranging from about 5 to about 1000 mPaxc2x7sec. Significantly, the preferred antifoaming silicone oil used in the present invention has a much higher viscosity, at least about 1500 mPaxc2x7sec and preferably at least 2500 mPaxc2x7sec, which is unexpectedly beneficial in an ink having a viscosity requirement that is a minor fraction of the viscosity found in screen printing inks. All of these viscosities are measured at 25xc2x0 C. Most significantly, antifoaming silicone oils useful in the present invention preferably are combined with particulate material, preferably having a particle size of about 0.001 micron to about 2 microns. Suitable particulate materials include silica particles, urea particles, micronized polyolefins, micronized polyolefin waxes, fluorinated polyolefin particles, micronized amorphous amide waxes, high molecular weight polyvinyl compound particles, polyamide particles, and mixtures thereof. Preferred particulates for use in the antifoaming oil include silica particles and urea particles. The particulatecontaining antifoaming agent is able to provide a means to reduce foaming without otherwise harming the flow properties of the ink contributed by the fluorochemical surfactant.
Therefore, unexpectedly, in preferred embodiments, minor amounts of a fluorochemical surfactant and a particulate-containing antifoaming agent combine to provide superior flow properties for a piezo ink that has considerable limitations on viscosity and flashpoint.
One aspect of the present invention is an organic solvent-based piezo ink, comprising: (a) a particulate material; (b) a binder; (c) an optional plasticizer; (d) an organic solvent; (e) a fluorochemical surfactant; and (f) an antifoaming agent comprising an oil; wherein the ink has a viscosity of less than 100 mPaxc2x7sec measured at 25xc2x0 C. and a shear rate of at least 1000 secxe2x88x921. In a preferred embodiment, the oil is provided in an antifoaming agent. Preferably, the antifoaming agent includes a silicone oil and a particulate material, wherein the particulate material has a particle size of about 0.001 micron to about 2 microns. Preferred particulate materials include pigment particles and/or antifoaming particles. Viscosity and shear rate are measured on a cone and plate rheometer according to techniques known to those skilled in the art.
Another aspect of the present invention is a method of making an ink formulation described above by dispersing a pigment chip into an organic solvent to form a pigment paste; and mixing into the same organic solvent or a different organic solvent the pigment paste, a binder, a plasticizer, a fluorochemical surfactant, and an antifoaming agent that includes an oil, and preferably a particulate material having a particle size of about 0.001 micron to about 2 microns. Pigment chips are pigments that have been predispersed into a binder (e.g., a vinyl resin, etc.).
Another aspect of the present invention is a method of using an ink formulation described above, comprising the steps of activating a piezo inkjet print head and ejecting drops of ink on demand of a size ranging from about 10 pL to about 150 pL from the piezo inkjet print head onto a polymer film.
A feature of the present invention is the ability to mix a variety of solvents, additives and stabilizers without adversely affecting flow of the ink.
Another feature of the present invention is the ability to use commercially available chemicals to formulate piezo inks of the present invention.
An advantage of the present invention is printing of excellent quality, large format, high resolution, image graphics without damage to piezo inkjet print heads but with excellent evaporation of organic solvents from the ink printed on media. This advantage is especially significant because the presence of the higher viscosity silicone oil is able to overcome the tendency of fluorochemical surfactants to foam during motion. The minimization of foam assures good flow of the ink through the piezo inkjet head that operates with bursts of abrupt motion to eject ink on demand onto the receiving substrate.
Another advantage of the present invention is the formation of image graphics of at least three years outdoor durability in vertical applications without the requirement of a clear coating or over laminate to protect such graphics. This advantage is especially significant because one component of the flow agents is a particulate such as silica that is otherwise known to provide porosity in an ink deposited on a receiving substrate. Thus, for this advantage, the benefits of the fluorochemical surfactant are unaffected in the resulting image graphic.
Another advantage of the present invention is the ability to adjust pigment and binder concentrations in the ink formulation to tailor viscosity of the ink to be accommodated in a variety of piezo inkjet print heads. This adjustment of viscosity does not otherwise adversely affect the balance of properties provided by the two types of flow agents used in the ink.
Another advantage of the present invention is the ability to use a variety of polymeric materials as plumbing components that are essentially unreactive with components in the ink formulation of the present invention, such that an expensive, large production piezo inkjet printer with multiple expensive print heads can be insulated from internal damage due to incompatible chemicals.
It should be understood that where incorporation of an ingredient is specified, either a single ingredient or a combination or mixture of materials may be used as desired.
Further features and advantages are identified in conjunction with a discussion of the following embodiments of the invention.
Receiving substrate
Materials suitable for use as the receiving substrate for inks of the present invention include, but are not limited to, paper, wood, glass, metal, cloth made of natural or synthetic fibers, and polymeric films. The films may be treated (e.g., flame treated) or untreated. Conventional polymeric films can be used directly as media for inks of the present invention. Nonlimiting examples of such films include single and multi-layer constructions of acrylic-containing films; ethyleneacrylic-containing films; melamine-acrylic-containing films; acrylonitrilebutadiene-styrene-containing films (ABS); poly(vinyl chloride)-containing films (e.g., vinyl, plasticized vinyl, reinforced vinyl, vinyl/acrylic blends); urethanecontaining films; melamine-containing films; polyvinylbutyral-containing films; polystyrene-containing films; polyamide-containing films (e.g., Nylon, etc.); polyester-containing films (e.g, polyethylene terephthalate (PET), polyethylene napthalate (PEN), etc.); polyester alkyd-containing films such as those available under the trade designation SCOTCHLITE ENGINEERING GRADE from 3M (St. Paul, Minn.); polyolefin containing films (e.g., polyethylene, polypropylene, etc.); polycarbonate-containing films; and multi-layered films having an image reception layer comprising an acid- or acid/acrylate modified ethylene vinyl acetate resin, as disclosed in U.S. Pat. No. 5,721,086 (Emslander et al.), the disclosure of which is incorporated herein by reference, or having an image reception layer comprising a polymer comprising at least two monoethylenically unsaturated monomeric units, wherein one monomeric unit comprises a substituted alkene where each branch comprises from 0 to about 8 carbon atoms and wherein one other monomeric unit comprises a (meth)acrylic acid ester of a nontertiary alkyl alcohol in which the alkyl group contains from 1 to about 12 carbon atoms and can include heteroatoms in the alkyl chain and in which the alcohol can be linear, branched, or cyclic in nature, as disclosed in copending, coassigned, U.S. patent application Ser. No. 09/109,471 (Emslander et al.), the disclosure of which is incorporated herein by reference.
Such films have two major surfaces with one surface being able to receive an inkjet image graphic of the present invention and the other major surface being adhered to a field of an adhesive, for example, a pressure sensitive adhesive. Usually, the field of adhesive on one major surface is protected by a release liner. Such films can be clear, translucent, or opaque. Such films can be colorless or solid color or a pattern of colors. Such films (typically with adhesive and liner) can have a thickness ranging from about 0.127 mm (5 mils) to as thick as can be accommodated by a commercial inkjet printer. Such films can be transmissive, reflective, or retroreflective. Such films can be as wide as can be accommodated by a commercial inkjet printer, allowing for the inks to suitably dry after printing, usually in a vertical alignment.
Commercially available films known to those skilled in the art include the multitude of PANAFLEX(trademark), NOMAD(trademark), SCOTCHCAL(trademark), SCOTCHLITE(trademark), CONTROLTAC(trademark), AND CONTROLTAC-PLUS(trademark) brand films and materials from 3M.
Printers
Ink formulations of the present invention are adaptable to be used with a variety of commercially available piezo inkjet printers. Nonlimiting examples of such printers include those identified above. These printers use different types of piezo inkjet print heads, including without limitation, those print heads identified above, and those manufactured by Tektronix of Wilsonville, Oreg.; Trident of Brookfield, Conn.; Spectra of Hanover, N.H.; and Microfab of Austin Tex. Two print heads often used are from Data Products and MIT printheads available from Xaar (United Kingdom).
Typically, such printers can print at speeds ranging from about 60 sq. ft/hr to about 600 sq. ft/hr (about 5.5 to 55 m2/hr) and preferably from about 90 to about 450 sq feet/hr and operate to print at widths ranging from about 1 foot to about 16 feet (0.30 m to 4.8 m) and preferably from about 3 to about 6 feet. At such speeds and widths, considerable amounts of ink are used to print image graphics, requiring reservoirs to store sufficient volumes of ink of various colors to make image graphics efficiently. The transport from reservoir to print head(s) requires plumbing which can not be damaged by the components in the ink formulation.
Inks of the present invention can avoid significant damage to the plumbing of the printer if that plumbing, such as tubing, valves, pumps and the like, is made from polyolefins (e.g., polyethylene or polypropylene); fluorinated polyolefins (e.g., polytetrafluroethylene (PTFE) and fluorinated ethylenes); glass; stainless steel; polyesters; PTFE-encapsulated silicone rubbers; polyimides, and hydrocarbon rubbers. Especially useful for such plumbing is an extrudable amorphous polyethylene that can be made optically clear, such as that material commercially available as Zeonex 250 polyethylene resin from Zeon Chemicals of Rolling Meadows, Ill., USA. Another useful material is polypropylene that can be assembled with adhesives.
Print heads deliver ink drops in nominal sizes of about 10 pL to about 150 pL and preferably about 20 pL to about 70 pL. The resolution of the inkjet image graphic is about 200 dots-per-inch (dpi) to about 800 dpi and preferably about 300 dpi to about 600 dpi.
Ink
Piezo inkjet printing principally relies on the use of four colors: cyan, magenta, yellow, and black (CMYK). However, to improve the resolution of images, some printers identified above also add two additional colors that are less concentrated relatives of the cyan and magenta inks, called xe2x80x9clight cyanxe2x80x9d and xe2x80x9clight magenta.xe2x80x9d Additionally, printers and software can be configured to use xe2x80x9cspecialxe2x80x9d or xe2x80x9cspotxe2x80x9d colors that are specific hues based on large usage or commercial branding requirements. For example, the color of red employed in branding of the corporate logo of 3M can be a special color. In addition, the inks of this invention may include colorless xe2x80x9cclear coatsxe2x80x9d that may be printed with an inkjet printer. Advantageously, the inks described herein are outdoor durable and maintain their light fastness.
Viscosities for solvent-based piezo inks of the present invention are less than 100 mPaxc2x7sec and desirably are less than 50 mPaxc2x7sec because of the requirements of the piezo print head. Preferred viscosities for solvent-based piezo inks will depend on the specific print head being used. However, a useful viscosity for common commercially available print heads is about 7 mPaxc2x7sec to about 30 mPaxc2x7sec, preferably about 7 mPaxc2x7sec to about 25 mPaxc2x7sec. All of these viscosities are measured at 25xc2x0 C. and a shear rate of at least 1000 secxe2x88x921. Of all of the properties of the ink formulation for solvent based inks, viscosity is the most critical because of the demands of the print head to operate properly with a liquid being ejected in such small volumes on demand. While the preferred ranges of viscosities are quite narrow, it is contemplated that, in the future, higher viscosities will be possible due to advances in piezo inkjet print heads. By comparison, the range of viscosity for press-ready solvent-based screen printing inks that are commercially available range from 1000 to 2000 mPaxc2x7sec at 25xc2x0 C. measured with a shear rate of at least 1000 secxe2x88x921. Not only are screen printing inks more than an order of magnitude more viscous, but also, the tolerance range of the acceptable viscosity is much less rigorous than that required for piezo inkjet inks. For that reason, components suitable for screen print inks are not automatic candidates for use in piezo inks. For example, screen print inks do use silicone oils but typically of a lower viscosity (5-1000 mPaxc2x7sec) as identified above. The selection of a higher viscosity oil for ink of the present invention is contrary to both the concern about the viscosity of the piezo ink, which must be finely tuned to the particular piezo inkjet print head within a narrow range, as expressed in preference above, and the concern that a higher viscosity oil would not disperse well or remain dispersed well in the ink.
Flash points for inks of the present invention can be at least about 1 42xc2x0 F. (61xc2x0 C.) and desirably are about 142xc2x0 F. to about 180xc2x0 F. (about 61xc2x0 C. to about 82xc2x0 C. A flash point of at least 142xc2x0 F. is above a regulation temperature for shipment of chemicals by air, which is very important in transportation costs and delivery timing for customers using such inks.
Percentage solids in inks of the present invention is preferably about 6% to about 15% because of the goal of maintaining the viscosity of the ink formulation within the range identified above. These percentage solids are considerably less than the typical 30-40 percent solids used in solvent-based screen printing inks because of the narrow range of viscosities that can be tolerated in a piezo inkjet print head.
Specific gravity at room temperature of inks of the present invention is preferably about 0.97 to about 1.13. Again the tolerances of piezo inkjet print heads dictate these ranges. The ratio of pigment:binder in inks of the present invention, depending on color and the use of xe2x80x9cstrongxe2x80x9d and xe2x80x9clightxe2x80x9d colors, is about 0.03:1.0 to about 0.90:1.0, and preferably about 0.03:1.0 to about 0.70:1.0.
In the art, a colorant is classified as either a pigment or a dye. A xe2x80x9cpigment,xe2x80x9d as used herein, can be an inorganic or organic, colored, white or black material that is practically insoluble in the medium (e.g., organic solvent) in which it is incorporated. A xe2x80x9cdye,xe2x80x9d unlike a pigment, dissolves during application and in the process loses crystal and/or particulate structure. It is thus by physical characteristic rather than by chemical composition that a pigment is differentiated from a dye (Industrial Organic Pigments Second Completely Revised Edition (Herbst and Hunger, Eds., page 1 (1997)).
Suitable pigment particle size based on volume distribution for inks of the present invention is about 0.06 micron (xcexcm) to about 0.50 micron and preferably about 0.2 micron or less. Another way of approximating dispersion properties is to measure pigment particle settling. This test uses a Byk Gardner Dynometer Plus instrument (commercially available from Byk Gardner of Columbia, Md.). After filtering to less than 0.5 micron particle size, it was found that particle settling ranged from about 1 mg to about 10 mg and preferably from about 1 mg to about 2 mg of pigment settling over 3 days. These particle settling data are especially unexpected because good values by this measurement range from less than 50 mg of pigment settling over 3 days to less than 60 mg of pigment settling over 5 days.
Surface wetting by the ink drop of the receiving substrate is an indication of flow for inks of the present invention. Suitable contact angles (as equilibrium contact angles on paraffin wax) are about 2xc2x0 to about 35xc2x0 and preferably about 14xc2x0 to about 22xc2x0.
Pigments
Pigments are a preferred class of colorants for use in the inks of this invention. As identified above, the number of colors can range from four basic colors to any number of special colors to augment printing needs for large volume image graphics.
The art of organic solvent-based screen print inks can be utilized for candidates as pigments for inks of the present invention. One skilled in the art can select commercially available pigments from suppliers such as Ciba Specialty Chemicals of Newport, Del., USA, and disperse these pigments into resins to produce xe2x80x9cchips.xe2x80x9d Alternatively, one can select from commercially available chips, such as vinyl-containing chips available from suppliers including Penn Color of Doylestown, Pa., USA. Nonlimiting examples of cyan pigments include IRGALITE GLG (Ciba Specialty Chemicals of Greensboro, N.C.) and SUNFAST 249-1284 (Sun Chemical Corporation of Fort Lee, N.J.).
Nonlimiting examples of magenta pigments include QUINDO magenta RV-6828 (Bayer of Pittsburgh, Pa.) and Magenta B RT-343-D (Ciba Specialty Chemicals).
Nonlimiting examples of yellow pigments include Fanchon Fast yellow Y5686 (Bayer) Fanchon yellow Y5688 (Bayer), and Sandorin 6GL (Clariant of Charlotte, N.C.).
Nonlimiting examples of black pigments include Pfizer lampblack LB-1011 (Pfizer of Easton, Pa.) and Raven 1200 (Columbian Chemicals of Atlanta, Ga.).
Pigments predispersed into a binder (xe2x80x9cchipsxe2x80x9d) are typically pre-mixed into pastes according to techniques known to those skilled in the art. Pastes may be prepared by dispersing a pigment chip in a solvent. Pigment chips selected from those identified above may be dispersed in a solvent or blends of solvents such as cyclohexanone, isophorone, butyrol lactone, m-pyrol, ethylene glycol butyl ether acetate (EB Acetate), or Exxate 600, 700, or 800 in a weight percent ratio of pigment to solvent of about 10:90 to about 50:50 and preferably about 25:75 to about 35:65. The paste may also contain other additives including, but not limited to, dispersants and binders as desired.
Suitable values for the weight percent of pigment pastes in inks are about 1 weight % to about 40 weight % and preferably about 1 weight % to about 25 weight %.
Binders
Binders are typically resins that are compatible with pigment particles such that upon evaporation of volatile components of the ink, the binders form films of the deposited pigments on the receiving substrate. Advantageously, the binders described herein are outdoor durable.
Nonlimiting examples of suitable binders are polymeric resins such as vinyl-containing polymers (e.g, VYHH, VYNS, VYHD, and VAGH brand vinyl-containing resins from Union Carbide) and acrylic-containing polymers (e.g., polymethylmethacrylate, polymethylbutylacrylate, polyethylmethacrylate and copolymers thereof). Preferred binders are Acryloid A11 and Acryloid B-66 brand resins from Rohm and Haas and VAGH brand resin from Union Carbide.
Suitable values for the weight percent of binders in inks are about 4.0 weight % to about 8.0 weight % according to desired pigment:binder ratios and durability requirements for the resulting image graphics in outdoor environments.
Radiation Curable Materials
For some applications, it may be desirable that the inks of this invention are radiation curable. For example, radiation-curable inks may be prepared by incorporating radiation curable materials including, but not limited to, monomers, oligomers, stabilizers, and optionally initiators and pigments into the ink. After the resulting inks have been applied to a receptor, they may be cured by exposure to radiation such as electron beam (e-beam) radiation. If photoinitiators or photocatalysts are also incorporated into the radiation-curable inks, the resulting inks may be cured after they have been applied to a receptor by exposure to actinic radiation such as ultraviolet (UV)- or visible-light.
Suitable monomeric and oligomeric materials useful in radiation-curable inks of the present invention include mono- and poly-functional acrylates and methacrylates including, but not limited to, isooctyl acrylate, lauryl acrylate, di(ethylene glycol) ethyl ether acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, phenoxyethyl acrylate, nonophenol ethoxylate monoacrylate, glycerol diacrylate, glycerol triacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol dimethacrylate, 1,3-propanediol dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,8-octanediol diacrylate, triethylene glycol diacrylate, triethyleneglycol dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, ethoxylated neopentyl glycol diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, trimethylolpropane propoxylate triacrylate, di(trimethylolpropane) tetraacrylate, 1,4-cyclohexanediol diacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, di(pentaerythritol) hexaacrylate, di(pentaerythritol) hexamethacrylate, bisphenol A epoxy diacrylate, bisphenol A ethoxylate diacrylate, urethane acrylate, urethane methacrylate, and combinations thereof. Preferred radiation-curing agents include oligomeric acrylate functional urethanes and acrylics. Suitable polymeric radiation-curing agents include acrylate-terminated polysiloxanes, polyurethanes, polyethers, polyesters, polyurethanes, etc.
Radiation-curable inks of the present invention may also contain photoinitiators. Many such materials are well known in the art. The photoinitiator can be any compound that produces a free radical on exposure to radiation such as ultraviolet or visible radiation and thereby initiates a polymerization reaction. Examples of suitable photoinitiators for use in radiation-curable inks of the present invention include, but are not limited to, anthraquinone and substituted anthraquinones such as alkyl substituted or halo substituted anthraquinones including 2-tert-butylanthraquinone, 1 -chloroanthraquinone, p-chloroanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, octamethylanthraquinone and 2-amylanthraquinone; other substituted or unsubstituted polynuclear quinones including 1,4-naphthoquinone, 9,10-phenanthraquinone, 1,2-benzanthraquinone, 2,3-benzanthraquinone, 2-methyl-1,4-naphthoquinone, 2,3-dichloronaphthoquinone, 1,4-dimethylanthraquinone, 2,3-dimethylanthraquinone, 2-phenylanthraquinone, 2,3-diphenylanthraquinone, 3-chloro-2-methylanthraquinone, retenequinone, 7,8,9,10-tetrahydronaphthaacenequinone, 1,2,3,4-tetrahydrobenzantracene-7,2-dione; acetophones such as acetophone, 2,2-dimethoxy-2-phenylacetophone, 2,2-diethoxy-2-phenylacetophone, 1,1-dichloroacetophone, 1-hydroxycyclohexylphenylketone, 2-methyl-1-(4-methylthio)phenyl-2-morpholinpropan-1-one, and 2-benzyl-2-(dimethylamino)-4xe2x80x2-morpholinobutyrophenone; thioxanthones such as 2-methylthioxanthone, 2-decylthioxanthone, 2-dodecylthioxanthone, 2-isopropylthioxanthone, 2,4-dimethythioxanthone, 2,4 diethylthioxanthone, 2-chlorothioxanthone, and 2,4-diisopropylthioxanthone; ketals such as acetophone dimethylketal and benzil dimethylketal; benzoins and benzoin alkyl ethers such as benzoin, benzoin methyl ether, benzoin isopropyl ether, and benzoin isobutyl ether; azo compounds such as azobisisovaleronitrile; phosphine oxides such as bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, and bis(2,6-dimethoxybenzoyl)(2,4,6-trimethylpentyl)phosphine oxide; and benzophones such as benzophenone, methyl benzophenone, 4,4xe2x80x2-dichlorobenzophenone, 4,4xe2x80x2-bisdiethylaminobenzophenone, Michler""s ketone, xanthones, and mixtures thereof. The selection of suitable photoinitiators will depend on the spectroscopic properties of the other ingredients in the ink including binders and pigments.
Solvents
Organic solvents suitable for use in the inks of the present invention include ketones, aromatic hydrocarbons, and esters (e.g., lactates, acetates, etc.). Examples of such solvents useful in inks of the present invention include cyclohexanone, propylene glycol monomethyl ether acetate (PM acetate), diethylene glycol ethyl ether acetate (DE acetate), isophorone, ethylene glycol butyl ether acetate (EB acetate), dipropylene glycol monomethyl acetate (DPM acetate), butyrol lactone, n-methyl pyrrolidone, alkyl acetate esters (such as those available under the trade designations EXXATE 600, EXXATE 700, and EXXATE 800 fluids from ExxonMobil Corp., Irving, Tex.), and combinations thereof. The amount of solvent is determined by the amount of other components in the ink formulation and is typically about 90 weight % to about 94 weight %.
Surface tension of solvents useful in the present invention can range from about 22 dynes/cm to about 36 dynes/cm when measured at 25xc2x0 C., the same temperature as used to determine viscosity.
Fluorochemical Surfactants
Fluorochemical surfactants in the present invention provide a critical element as a flow agent to lower the surface tension of solvents. The lower surface tension allows the inks to flow out better on the receiving substrate. Such fluorochemical surfactants are solutes in solvents used in the present invention.
Nonlimiting examples of fluorochemical surfactants include the family of FC branded chemicals from 3M and preferably includes FLUORAD FC430 and FC431. Such chemicals are fluorinated alkyl esters.
Suitable values for the weight percent of such fluorochemical surfactants in inks of the present invention are about 0.1 weight % to about 0.5 weight % and preferably from about 0.20 weight % to about 0.30 weight %.
Antifoaming Agent
The antifoaming agent includes an antifoaming oil and preferably a particulate material. The antifoaming agent may be dispersed in solvents used in the present invention to aid in minimizing foaming that might otherwise occur using the fluorochemical surfactants according to the present invention. The antifoaming oils of this invention are preferably viscous, substantially water-insoluble liquids that can alter the surface tension of a fluid at room temperature. The antifoaming oils used in the present invention are preferably substantially non-drying oils (i.e., they do not significantly absorb oxygen to become hard and resinous upon exposure to air) and are substantially non-film-forming fluids (i.e., they do not generally form a coherent film when a solution of the oil in solvent is coated as a thin layer and the solvent is evaporated) at room temperature. Such oils preferably are not crosslinked and are generally stable in air. This is in contrast to a silicone resin binder, such as DOW CORNING 6-2230 (a highly crosslinked solid and film forming agent at room temperature).
Antifoaming oils suitable for this invention include, but are not limited to, mineral oils and silicone oils. Mineral or paraffin oils are available under trade designations such as WHITE OIL, TECHNICAL WHITE OIL, and NUJOL from a variety of suppliers including Fisher Scientific (Fair Lawn, N.J.), J. T. Baker (Phillipsburg, N.J.), and Witco Chemical Corp. (Greenwich, Conn.). A preferred antifoaming oil for use in the present invention is an antifoaming silicone oil.
Nonlimiting examples of antifoaming silicone oils include Paint Additive 11 brand silicone oil (Dow Chemical of Midland, Mich.), SF96-5brand silicone oil (General Electric (GE) of Waterford, N.Y.), SF69 brand silicone oil (GE), Silwet L-77 brand silicone oil (OSI of Danbury, Conn.), L-7657 brand silicone oil (OSI), Dow Corning Antifoam 1400 brand silicone oil (Dow Corning, Midland, Mich.) and AF9000 brand silicone oil from GE.
Although it is preferable to have particulate material such as silica contained within the antifoaming oil from the manufacturer, antifoaming oils that do not contain any particulate material such as silica can readily be employed by adding particulate material. Suitable particulate materials include silica particles such as those present in the silicone oil commercially available under the trade designation AF9000 from GE; urea particles (Byk Chemie, Wallingford, Conn.); micronized polyolefins (Lubrizol Corp.,Wickliffe, Ohio); micronized polyolefin waxes (Lubrizol Corp.,Wicklife, OH); fluorinated polyolefins (e.g., fluorinated polyethylene, polytetrafluoroethlyene (PTFE, Dupont Corp., Wilmington, Del.)); micronized amorphous amide waxes (Lubrizol Corp.,Wickliffe, Ohio); high molecular weight polyvinyl compound particles available under the trade designation LANCO ANTIBUBBLE LT from Lubrizol Corp. (Wickliffe, Ohio); polyamide particles available under the trade designation ORGASOL from Elf-Atochem (Philadelphia, Pa.); and mixtures thereof. Preferred particulates for use in the antifoaming oil include hydrophobic silica particles (i.e., silica particles that exhibit hydrophobic properties when wetted by silicone oil) and urea particles. Suitable particulate material typically has a particle size of about 0.0001 micron to about 2 microns. Preferably, the particle size is from about 0.001 micron to about 2 microns.
The viscosity of oils useful in the present invention can be at least 5 mPaxc2x7sec at 25xc2x0 C. Preferably, the viscosity is about 1000 mPaxc2x7sec to about 30,000 mPaxc2x7sec at 25xc2x0 C.
Suitable values for the weight percent of the antifoaming agent, preferably in the form of the particulate-containing antifoaming oils, in inks of the present invention are about 0.005 weight % to about 1.0 weight % and preferably about 0.01 weight % to about 0.9 weight %.
The preferred particulate-containing antifoaming agents used in the present invention provide an unexpected balance of properties. A suitable amount of particulate material dispersed in the antifoaming agent is about 10 weight % to about 50 weight %, making the total amount of particulate contained in the ink to be about 0.005 weight % to about 0.5 weight %. Yet the presence of such particulate material does not adversely affect the flow agent properties or the clear coating effect of the inks as contributed by the fluorochemical surfactant. Moreover, as explained above, the use of a higher viscosity oil (e.g., polydimethylsiloxane silicone oil) in combination with particulate material (e.g., silica particles) unexpectedly provides antifoaming properties without adversely affecting the other performance properties of the ink being jetted or once on the receiving substrate.
Plasticizers
The optional plasticizers are typically polyesters that are compatible with the vinyl and acrylic resins and any other binder used along with thc stabilizers and flow agents such that upon evaporation of volatile components of the ink, the plasticizers aid the flexibility of the film formed from the deposited binder with pigments on the receiving substrate. The plasticizer also becomes part of the final ink film.
Nonlimiting examples of suitable plasticizers include UNIFLEX 312 brand plasticizer (Union Camp of Wayne, N.J.), PARAPLEX G-31 brand plasticizer (C. P. Hall of Chicago, Ill.) and PARAPLEX G-51 brand plasticizer (C. P. Hall).
Suitable values for the weight percent of plasticizers in inks of the present invention are about 0.1 weight % to about 4.0 weight % and preferably about 0.2 weight % to about 2.0 weight %.
Optional Heat and Light Stabilizers
To enhance durability of a printed image graphic, especially in outdoor environments exposed to sunlight, a variety of commercially available stabilizing chemicals can be added optionally to inks of the present invention. These stabilizers can be grouped into the following categories: heat stabilizers; ultra-violet light stabilizers; and free-radical scavengers.
Heat stabilizers are commonly used to protect the resulting image graphic against the effects of heat and are commercially available as Mark V1923 brand stabilizer (Witco of Houston, Tex.), Synpron 1163 brand stabilizer (Ferro of Cleveland, Ohio), Ferro 1237 brand stabilizer (Ferro), and Ferro 1720 brand stabilizer (Ferro). Such heat stabilizers can be present in about 0.02 weight % to about 0.15 weight%.
Ultra-violet light stabilizers are commercially available as UVINOL 400 brand benzophenone uv-absorber (BASF of Parsippany, N.J.) and TINUVIN 900 brand uv-absorber (Ciba Specialty Chemicals) and can be present in about 0.1 weight % to about 2.0 weight % of the total ink.
Free-radical scavengers can be present in about 0.05 weight % to about 2.0 weight % of the total ink. Nonlimiting examples of the scavenger include hindered amine light stabilizer (HALS) compounds, hydroxylamines, sterically hindered phenols, and the like. Preferably, the free-radical scavenger is regenerating such as exists with the HALS compounds. Commercially available HALS compounds include Tinuvin 292 hindered amine light stabilizer (Ciba Spccialty Chemicals) and Cyasorb UV3581 hindered amine light stabilizer (Cyanamid of Wayne, N.J.).
Mixing Ink Formulations
Conventional mixing techniques are used to mix the pigment paste with the various other components in the inks. Typically, such mixing techniques use a high shear dispersing blade operating at such speeds for such times as completely to disperse and dissolve the chips into the solvent. The pastes are then blended in with solvents, stabilizers, flow agents, and some resin solutions according to mixing techniques known to those skilled in the art using a conventional mixing blade. After a thorough mixing, the inks are filtered and then packaged. The nature and amount of solvents can be varied according the pigments employed.
Using Ink Formulations
Once mixed, the inks of the present invention have a stabilized shelf life acceptable for use in large volume piezo inkjet printing. Preferably, such inks can be used in piezo inkjet printers produced by Raster Graphics, Idanit Co. Ltd., and the like, although some variations will be necessary to optimize the formulations of such inks for use in different printers. More particularly, the inks of the inventions may be formulated according to the specifications and performance requirements of print heads. For example, inks prepared in the following examples were tested using MIT print head made by Xaar (United Kingdom), both at nominal 20 pL and nominal 70 pL drop sizes. It is contemplated that other print heads will require different viscosities and other minor adjustments to the formulation without departing from the scope of the present invention.
The presence of two different types of flow agents: fluorochemical surfactants and particulate-containing oil antifoaming agents accomplish the purposes of the present invention that only one of them could not accomplish.
While not being limited to a particular theory, the fluorochemical surfactant minimizes the use of silicone oils as flow agents which have the disadvantage of slowing evaporation of solvents on the receiving substrate when present in high concentrations, e.g, above about 0.1 weight percent. Yet the tendency of the fluorochemical surfactant to foam during agitation and motion is counteracted by a minor amount of a high viscosity oil that also contains particulate material, such as silica particles. This fine balance of properties for flow permits a superior piezo inkjet ink with outdoor durability and minimizes the need for overlaminates or clear coats.
Moreover, keeping the flashpoint above about 61xc2x0 C. (142xc2x0 F.) permits inks of the present invention to be shipped with less regulatory restrictions.